The Effects of Alkaline pH on Microleakage of Mineral Trioxide Aggregate and Calcium Enriched Mixture Apical Plugs.

Statement of the Problem: Alkaline pH can affect the physical and chemical properties and sealing ability of apical plug material. Calcium hydroxide is used in non-vital teeth as an intracanal medication to complete disinfection of root canals. It raises the pH of environment to alkaline value. Purpose: The aim of this in vitro study was to evaluate and compare the effect of alkaline pH on the sealing ability of calcium-enriched mixture (CEM) cement and mineral trioxide aggregate (MTA) apical plugs. Materials and Method: Seventy single-rooted human maxillary anterior teeth were randomly divided to two experimental groups for Angelus MTA and CEM cement (n=30) and two control groups (n=5). Each group was divided into two subgroups of 15 for neutral and alkaline pH, and 1 negative and 1 positive control groups of 5. The root canals were cleaned and shaped by using ProTaper rotary system (Dentsply Maillefer; Ballaigues, Switzerland) and the terminal 3mm of the roots were resected. Then, MTA and CEM cement were condensed in apical region with 3mm thickness. The samples were exposed to two environments with different pH values of 13 and 7.4. The leakage was assessed by using the fluid filtration technique at 1, 7, 14, 30 days intervals. Data were analyzed by the repeated measures MANOVA. Results: There was no statistically significant difference in the rate of microleakage between neutral and alkaline pH of CEM cement and MTA ( p > 0.05). The sealing ability of MTA in an alkaline pH of 13 was significantly less than CEM cement in this pH ( p < 0.05). Conclusion: An environment with alkaline pH had no adverse effect on the sealing ability of MTA and CEM cement used as apical plugs. CEM cement had better sealing ability in alkaline pH. Key Words: Alkaline pH; Apical Plug; Calcium Enriched Mixture Cement; Fluid Filtration; Mineral Trioxide Aggregate; Microleakage; Sealing Ability


Introduction
A non-vital immature tooth presents many complications to achieve an appropriate endodontic therapy. [1] Since the apex is extremely wide, no barrier exists to limit the obturation process of the root canal system. [1][2][3] A variety of materials including mineral trioxide aggregate (MTA) and calcium-enriched mixture (CEM) cement have been used to create an apical stop in such cases. MTA has a good sealing ability, sets in the presence of blood and it is also biocompatible; all these properties make it a good candidate for apical plug. [4] However, it encompasses some drawbacks such as extended setting time, poor handling, and high cost.
[5] On the other hand, CEM cement has good sealing ability and favorable biologic response, as well as greater flow, less film thickness [6-7] and shorter setting time (less than 1 hour) than MTA. [6][7][8] The vast majority of non-vital teeth are infected, so the first phase of treatment is to disinfect the root canal system. A creamy mix of calcium hydroxide is used as an intracanal medication to complete disinfection of the root canals. [9-11] Calcium hydroxide kills bacteria, neutralizes the biologic activity of lipopolysaccharides and makes the necrotic tissues more susceptible to the solubility action of NaOCl.
[10] Freshly-mixed calcium hydroxide produces an environment with alkaline pH. [12] It is impossible to remove all of the calcium hydroxide from the dentinal walls; so, the alkaline pH of this area can potentially affect the properties of freshly-applied apical plug materials. [10,13] This pH conversion inhibits the setting reactions and increases the solubility of materials.
Physical and chemical properties of materials affect their sealing ability. [14][15][16] Saghiri et al. [17] showed that the leakage of MTA in acidic pH occurred faster than in neutral pH. Lotfi et al. [11] concluded that alkaline pH affected the sealing ability of MTA.
Hachmeister et al. [18] found that calcium hydroxide did not influence the sealing ability of gray MTA (GMTA). Stefopoulos et al. [19] reported that calcium hydroxide pretreatment adversely affected the sealing ability of MTA.
To the best of our knowledge, no investigation has evaluated the effect of alkaline pH on the sealing ability of CEM cement. Therefore, the aim of this in vitro study is to assess the effect of alkaline pH on the microleakage of MTA and CEM cement by employing fluid filtration technique.

Materials and Method
Seventy extracted human maxillary single-rooted teeth were collected. After extraction, the teeth were placed in 1% sodium hypochlorite for 48 hours to be disin-   All experimental groups demonstrated various amounts of microleakage (Table 1). There was no statistically significant difference in RML between neutral and alkaline pH of CEM cement (p> 0.05). There was no statistically significant difference in RML between the neutral and alkaline pH of MTA (p> 0.05).
This materials exhibited similar sealing ability in neutral pH. The RML of MTA in an alkaline pH of 13 was significantly greater than CEM cement in the same pH (p< 0.05).The RML reduced over time and it was more detectable in the second interval ( Figure 1).

Discussion
This study compared the sealing ability of MTA and CEM cement as apical plugs in alkaline pH. Using calcium hydroxide as an intracanal medicament is effective in killing microbial flora and dissolving necrotic pulp tissue. [22][23]

Conclusion
Based on the results of this in vitro study, an alkaline pH environment had no adverse effect on the sealing ability of MTA and CEM cement as apical plugs.
CEM cement had better sealing ability in alkaline pH.